Method of making enamel coated articles



April 15, 1947. R. E. HARR 2,418,932

METHOD OF MAKING ENAMEL COATED ARTICLES Filed Nov. 13. 1940 wvmrm 7RLIHARR a); Arro'k/vir Patented Apr. l5, 1947 UNITED STATES PATENTOFFICE METHOD OF MAKING ENAMEL COATED ARTICLES Russel E. Harr, Chicago,Ill., assignor to Western- Electric Company. Incorporated,

New York,

Y., a corporation of New York Application November 13, 1940, Serial No.365,453 4 Claims. (Cl. 204-38) This invention relates to methods ofmaking enamel coated articles.

' An object of the invention is the provision of. improved methods forthe production of articles having a metal base and a smooth, highlyornamental and serviceable coating of vitreous enamel on the base.

' The present invention is particularly adapted to the product on ofarticles such as the number plates incorporated in telephone dials,which comprise a ase and a coating of vitreous enamel sued in articlesof this type. The enamel on numberplates must be highly adherent towithlarly important that the enamel have a smooth, even and unbrokensurface. Number plates are often exposed to dirt-laden atmospheres inservice and under these conditions even minute imperfections in theenamel surface tend to acculint and the like, which mars from theirutility. Because of these requirements and limitations, it has beencustomary to employ intermediate an improved 'process for forming thisnickel-iron alloy.

In accordance with one embodiment of the invention, a base of desiredshape is first formed of sheet iron and then copper plated, after whicha layer of nickel-iron alloy is electrodeposited on the copper. Thealloy layer is produced in an is applied base is then fired at fuse theenamel into on-the alloy layer and the asuitable temperature to acoating, v

A more complete understanding of the invention may be had by referenceto the following de- .Or grit, around 90.1n'esh tailed description,taken accompanying drawing,

Fig. 1 is a plan view of ing the invention, and Fig. 2 is an enlargedsectional view of the number plate taken on the line 2-2 of Fig. 1.

' Inthe first operation for producing a complete in which copper can beapplied conveniently in a conventional copper cyanide electroplating-process and a coating weight around 20 milligrams per square inch'isgenerally satisfactory. I

In the next operation, a nickel-iron alloy I2 is electrodeposited overthe copper in a uniform layer. The iron content ofthe alloy should bebetween 50% and 10.0% with the balance nickel and the best results aresecured with an alloy having an iron content around 1.5%.

To apply an alloy containing 1.5% iron and the balance nickel, anaqueous bath of the following composition is first prepared:

' Ounces per gal. of solution Nickel sulphate 24.0 Sodium chloride ;13.0 Boric acid 4,0 I Ferrous sulphate .0666 The solution is placed inthe tank of a conven.-.

a cloth bag, and then 'suspen'ding the container in the solution. aSeveral ba s of iron particles may be suspended in the solution, thedistribution "ofthe bags depending upon the size andarrangeinconjunction with the a number plate embody ment of the tank. Thepresence of oxidized iron (ferric oxide) in the plating solutionproduces an alloy which causes enameling defects when enamel is laterapplied thereto. The addition of metallic iron to the bath reduces theferric oxide to ferrous oxide which is not detrimental to the productionof. a satisfactory nickelriron. alloy. The copper plated bases arethensuspended. the solution and current applied until an alloy coatingof desired weight is electrodeposited on: the copper. The process isoperated ata temperature between 135 F. and 145*F': and a'currentdensity between 40 and 60 amperes per square foot of cathode sur-face-..The means. of; these values are used preferably.

The above temperature and current densityranges are critical and theirinterrelation is im.- portant. A variation in current density; forexample, will affect the proportions of irorr inthe deposited alloy fora given solution and temperature, as wellas. the properties oi the.alloy,. and for best results the above combination of solutionconcentrations,. operating; temperatures. and current densities shouldbe maintained. The. described solution will produce an alloycontainingabout 1.5% iron. If an alloy having a lower or higher iron content isdesired. the bath is. correspondingly adjusted. by the use of. less-rmore ferrous sulfate. or anodesr After. the copper. and. the: alloycoatingshave been: deposited on-the: base, the base. is ready.- to.receive the enamel, which is' applied only on. the face of the ring, orthe portion exposed. in service, in order to'minimize the. cost, of.the. article and also to" facilitate: the maintenance: of over-alldimensional tolerances. A coating of white enamel. l3, such. as a leadhero-silicate enamel opacified with arsenic oxide, is: applied first-The. enamel isdistributed on. the alloy surface either. in the form: ordry powder or by a wet process intwhichlthe enamel particles are mixedwith. water and a' flotation agent; such as-clay.. Thebase. is theirfiredsat. a temperature around 1-600 F. for" about three. and; one-halfminutes to fuse the: enamel.. I

Identifying characters in contrasting-colors: are usually required tocomplete the. plate. The application of these charactersusuall-yinvolves repeated refiring of the initial enamel coating and thispractice tendsto aggravate.

or other imperfections present in the initial coatine.

Orretype of plate, shown in the drawing has a background l4, letters andnumerals it. These characters are produced with an inky suspensionof:colored metallic oxides or frits in. avehicle-such as linseed oil andare applied on the surface of the white enamel by a: pri ting operation.The background,, which may be blue or black, is applied first and theplate is then baked at about '1'300F. to harden the ink' so that it willnot be marred in subsequent printing. operations; The letters; whichare" usually black; are then applied and the. plate is then again bakedat a temperature of about 1300 F. The numerals are usually colored redand are applied the. same manner, after which the. entire plate is againfired to. fully. mature the ceramic ink whichv requires exposure. to. atemperature around.1300' F. for approximately 415' minutes.

Theresultant enamelcoatingis highly adherent and. has a smooth and.continuous surface- In .enameling; number plates the peripheral edgeportions. of the enamel surface are critical and plates produced; byprior methnds have tended any roughness to develop a defect commonlyknown as "edge pimpling in these areas. These pimples may be very smalland difilcult to detect, but after a period of service, they accumulatedirt and other foreign material to form smudges which are very dificultto remove, particularly because the number plates are-not. readilyaccessible for cleaning after they are. assembled. in a dial.

The nickel-iron alloy layer produced as herein: described causes theenamel to fuse into a smooth coating without the formation of pimplesanywhere on the coating surface. The initial coat, of white enamel, isglassy and free of pimples. and these desirable surface conditions aare; preserved. during any refiring operations employedi the applicationof characters on the enamel. Theaction of the metallic iron ondepositi'on of the alloy under the prescribed operating conditionscontributes largely to the desired alloy properties and, as stated, thismetallic iron is. preferably provided in the form. of. smalL particles.

For. most applications,. a. coating weight of 20 milligrams persquareinchfor both the copper. and the alloy. is satisfactory, although. itmaybe desirable to vary these. values somewhat for. different enamelcompositions, and,. in general, the copper. and. alloy layers. shouldbeof. about equal weight.

Although the. invention has been. described. in connection with. themanufacture. of number plates. for. telephone. dials,. itwill' be.apparent. that is equally applicable. to other ornamented. enameledarticles anda it isto. beunderstood that the. invention is limited only.by the. scope. of. the appended claims.

What. is..claime.d is:

1.. A. method of. coating an article with a vitrifia-ble material whichcomprises electrodepositing. a. layer oi nickel-iron alloy containingfrom. .5I%- to 1. 0% of iron on..the article in a nickel sulfate,ferrous. sulfate solution, employing anickel anode. andan. ironanode,maintaining a quantity of metallic iron in. a subdivided-state. in the.solution. applying a. vitri-fiable material on the alloy layer, and.heating. the article to fuse the. vitrifiable; material tov form asmoothcoating.

2.4 A method of coating an article with. a vitrifiable material whichcomprises electrodepositing a layer of nickel-iron alloy containing from.5-%, to 10 of ironon the. article in a nickel sulfate, ferrous sulfatesolution, employing a nickel anode. and an iron anode, placing aquantity ofmetallic. iron in. addition to the iron anode in thesolution, applying a vitrifiablemateria-l on the alloy layer, andheating, thev article to fuse the vitrifiable material to form a smoothcoating.

3-..A method of coating an article with a vitrifiable material whichcomprises applying a layer of copper onthe article, electrodepositing alayer of nickel-iron alloy containing from .5-% to 10% of iron on the:article ina nickel sulfate, ferrous sulfate solution, employing a.nickel anode and an iron. anode, placing particles of metallic iron in.the solution during the. electrodeposition, applying a, currentdensityof between 40 and. 60 amperes per square foot to. the surface beingcoated at a. temperature of. F. to. 1.45. E, covering the. surface ofthe electrodeposited alloy with a vitrifiable material, and heatingthearticle to fuse the vitrifiable material to form. a. smooth coating.

4. A method of coating a ferrous base article with a vitrifiablematerial which comprises applying a layer of copper to. the. ferrouabase,

RUSSEL E. HARR.

REFERENCES CITED The following references are of record in the file ofthis patent:

Number J I v l 'I I UNITED STATES PATENTS Name Date Ketcham Sept. 2,1902 Eimen Jan. 6, 1925 Burns et a1 Dec. 22, 1931 Scott Nov. 12, 1935Fink Nov. 1, 1932 Cowper-Coles Feb. 9, 1915 Crowder Sept. 27, 1938Ramage Oct. 31, 1911 OTHER REFERENCES Cir. Bureau of Standards, No. 100(1924), p. 9,

